Microsurgical instruments for minimally invasive surgery have to meet particular demands specifically as regards a high degree of precision and the ability to control them ergonomically (i.e. with optimized control forces and kinematics) and using one hand. Minimally invasive surgery is increasingly being used for interventions which hitherto required opening the body of the patient at the appropriate locations, since with this surgery it is possible largely to avoid the negative effects of trauma.
The prior art discloses the use of microsurgical instruments in microsurgery, e.g. in endoscopic cardiovascular surgery. These microsurgical instruments comprise a tool which is arranged distally on a guide shank and which is in most cases composed of two jaws, of which at least one is movable, and an actuation grip which is mounted proximally on the guide shank and which is operated by the surgeon. The microsurgical instrument, along with its actuation grip, can be designed such that it can be actuated ergonomically by the surgeon; the control displacements performed on the actuation grip by the surgeon should be translated into the shortest possible working displacements of the tool. Such an actuation grip is often designed as a “forceps handle”, i.e. the surgeon holds and actuates the actuation grip like forceps or scissors.
DE 695 32 918 T2 discloses a microsurgical instrument having a known one with a forceps grip. It has an outer shank and an inner shank, which are movable relative to each other. A surgical tool, which can be controlled by the relative movement of the shanks, is mounted on a distal end. An adjustment member with two symmetrical levers is arranged at the proximal end of the outer shank for the purpose of manipulating the tool. At a pivot point, which lies closer to the proximal end than to the distal end of the levers, the levers are coupled to one of the two shanks, the outer shank or the inner shank, wherein the proximal ends of the levers are connected pivotably to the respective other shank. One end of an elongate connection member is mounted pivotably at the pivot point of the levers, wherein the respective other ends of the connection members of the two levers are mounted rotatably on a common pin on one of the two shanks. During a pivoting movement of the levers, this pin moves in an axial direction, as a result of which the tool can be actuated, i.e. it is a simple scissor hinge which is controlled directly by the levers. In a lever excursion by a fixed amount, a mechanism of this kind for converting a pivoting movement of the levers into an axial movement leads to a much greater axial excursion when the levers are positioned closely than when the levers are positioned wide open, and the maximum possible transmission ratio is greatly limited.
DE 10 2010 013 916 A1 also discloses such an instrument which is actuated by means of a forceps grip which is present at the proximal end of a hollow shank, and at the distal end it has a surgical tool which is actuated by means of the grip via an actuating rod that is mounted so as to be axially movable in the shank. The levers are operatively connected to the actuation rod via a pin-and-slot control system, at the proximal end of which arms are arranged which protrude outward at right angles and at whose ends control pins are present. These are guided in guide tracks or guide grooves in the grip parts of the handle, wherein the guide tracks are at an acute angle with respect to the longitudinal axis of the hollow shank in a rest position and, during a pivoting movement of the levers, convert this movement into an axial movement of the actuation rod. This mechanism too has a not entirely homogeneous transmission ratio, which reduces the control precision. In addition, the maximum possible transmission ratio is relatively small, and the mechanism is expensive to produce and susceptible to production fluctuations. The partially open mechanism is susceptible to contamination and, during an operation, can become jammed on a trocar sleeve or an incision opening, which greatly restricts the freedom of movement of the operating surgeon.